Among the number of diphenylhydantoin derivatives which were synthesized last year, three were tested for their capacity to induce gingival hyperplasia in ferrets and to induce cleft palate in mice. When ferrets were fed a diet containing 0.5 mg of diphenylhydantoin derivatives daily for 7 weeks, the incidence of gingival hyperplasia was 40-75% lower in the animals fed deca deutero diphenylhydantoin or monofluoro phenyl-phenylhydantoin than in those fed diphenylhydantoin. When the same animals were fed a diet containing 2 mg daily for an additional 6 weeks, deca deutero diphenylhydantoin induced about 300% higher incidence of gingival hyperplasia than diphenylyhdantoin. Moreover, the incidence of hyperplasia caused monofluoro phenyl-phenylhydantoin or pentadeutero phenylphenylhydatoin was 30-60% higher than that caused by diphenylhydatoin. These derivatives were tested for induction of cleft paflate in mice liters at 75,100 and 150 mg/kg i.m. on the 11th day of gestation as a ingle administration to the mother, all derivatives except pentadeutero phenyl-phenylhydatoin induced high incidence of cleft palate (60-90%) at 100 mg/kg. All derivatives had 2-3 fold higher rate of resorption as diphenylhydantoin.